Bromine Hofmann reaction

The Hofmann reaction of an amide with bromine and alkali apparently goes by way of the iV-bromoamide and unicovalent electron-deficient nitrogen. 

The Lossen rearrangement of an hydroxamic acid under basic conditions is a variant of the Hofmann reaction in which the aroyloxy group fills the role of the bromine.314... 

Further Experiments.—A solution of urea is made alkaline with sodium hydroxide solution and is then shaken with a few drops of bromine. Nitrogen is evolved. Compare, in this connexion, the Hofmann reaction (p. 155). 

By the action of hypobromite on the —CONH2-group one hydrogen atom of the NH2-group is replaced by bromine. The first product of the Hofmann reaction, the N-bromoamide, can be isolated in certain cases. 

Hofmann reaction org chem A reaction in which amides are degraded by treatment with bromine and alkali (caustic soda) to amines containing one less carbon used commercially in the production of nylon. haf-mon re,ak-sh3n )... 

Another example is the Hofmann reaction in which an amide is converted to an amine having one fewer carbon atoms (Equation 2.6 and Scheme 2.11). The reaction is usually initiated by adding the amide to cold alkaline sodium hypobromite solution (bromine and aqueous NaOH), followed by rapid warming [22] ... 

In the Hofmann reaction (Scheme 8.2), an amide is treated with a halogen, usually bromine, in alkali in which the reactive species is the hypohalite ion (XO ). This reaction, which applies to aliphatic as well as aromatic amides, has been thoroughly studied. Evidence supporting... 

The reaction is accomplished by simply heating together phthalic anhydride and ammonium carbonate. Phthalimide then hydrolyzes with potassium hydroxide yielding the potassium salt of phthalamidic acid and this acid amide compound undergoes the Hofmann reaction (pp. 148, 685) with bromine (or chlorine) and potassium hydroxide by which one of the carboxyl groups is replaced by the amino group yielding amino benzoic acid or anthranilic acid. 

Isocyanates, the initial products of the Hofmann rearrangement, usually undergo solvolysis to give amines, as described earlier (Section 4.4.1.1). However, a two-phase Hofmann reaction using phase transfer catalysts allows isolation of reactive isocyanates (equation 12). The phase transfer catalyst is essential for the formation of primary and secondary isocyanates, while tertiary isocyanates are formed without the catalyst. Shorter reaction times at room temperature as well as high dilution conditions minimize the formation of by-products such as dialkylureas or acylalkylureas. Chlorine in place of bromine considerably decreases the yield of isocyanates. 

An attempted Hofmann reaction of phosphonoacetamides (22) with alkaline sodium hypobromite shows a dramatic substituent effect (Scheme 10). The rearrangement occurs when the alkyl residue (R) is ethyl or phenyl, while only bromination occurs when R is hydrogen or benzyl. 

Hofmann reaction. In the preparation of 3-aminopyridine from nicotinamide, bromine is added to an aqueous solution of sodium hydroxide with stirring in a... 

The Hofmann reaction is capable of general application. By use of it, the primary amine of the next lower series may be obtained from any acid-amide, since the elimination of carbon dioxide takes place-With the higher members of the series, the reaction in part proceeds still further, since the bromine acts upon the primary amine to form a nitrile ... 

The action of bromine and alkali on amides to form amines containing an atom of carbon less, was discovered by Hofmann. Another Hofmann reaction , now called exhaustive methylation , was applied to convert piperidine into an unsaturated hydrocarbon piperylene, CgHg. (The simplest case, the decomposition by heat of tetraethylammonium hydroxide (C2H5)4N0H = (C2Hs)3N + C2H4 + H2O, he discovered in 1851 see p. 440.)... 

Hofmann (reaction of a primary amide with alkaline bromine solution) o... 

The Hofmann Rearrangement (HR), which is often called the Hofmann Reaction or Hofmaim Degradation but should not be confused with the Hofmann Elimination, describes the multistep transformation of a primary carboxamide 1 to a primary amine 3 via an intermediate isocyanate 2 under the action of bromine and sodium hydroxide. " As will be shown, many variations of this rearrangement are known and widely used today. 

In the Hofmann reaction an amide is converted to an amine of one less carbon atom by treatment with bromine (or chlorine) and alkali. In effect the carbonyl group of the amide is eliminated. The reaction is... 

Special Conditions for the Hofmann Reaction of Higher Aliphatic Amides and of a,p-Unsaturated Amides. As mentioned earlier, amides of the higher aliphatic acids are converted to the corresponding amines in poor yield by the usual technique. Such amides, however, are smoothly converted to methyl carbamates if bromine (1 mole) is added rapidly with thorough mixing to a methanolic solution of the amide (1 mole) containing sodium methoxide (2 moles). 

Our recent studies on effective bromination and oxidation using benzyltrimethylammonium tribromide (BTMA Br3), stable solid, are described. Those involve electrophilic bromination of aromatic compounds such as phenols, aromatic amines, aromatic ethers, acetanilides, arenes, and thiophene, a-bromination of arenes and acetophenones, and also bromo-addition to alkenes by the use of BTMA Br3. Furthermore, oxidation of alcohols, ethers, 1,4-benzenediols, hindered phenols, primary amines, hydrazo compounds, sulfides, and thiols, haloform reaction of methylketones, N-bromination of amides, Hofmann degradation of amides, and preparation of acylureas and carbamates by the use of BTMA Br3 are also presented. 

The N-bromination of amides with bromine and alkali has been extensively researched as the first step of the Hofmann degradation. However, it is difficult to isolate the N-bromoamides because of their subsequent reaction to produce amines, which proceeds very readily under excessive alkaline conditions. Now, the reaction of amides with a stoichiometric amount of BTMA Br3 and sodium hydroxide in ice-water gave N-bromoamides in fairly good yields. Our method can be applied to various types of aliphatic, aromatic, and heterocyclic amides (Fig. 31) (ref. 39). 

Reaction between amides, bromine, and alkoxides (Hofmann), and... 

Electrolysis of amides in MeOH containing the bromide ion efficiently led to products of the Hofmann rearrangement (for example, 119 to 120 Scheme 43) [131]. This reaction, named the electrochemically induced (E-I) Hofmann rearrangement, is achieved without any bromine and base under mild and neutral reaction conditions. 

---